Panes of glass are often beveled to improve their appearance. Beveling a pane of glass involves removing a portion of the glass to give the pane a more ornate and aesthetically pleasing appearance. Bevels generally include a height, a width and a bevel angle or pitch. For example, and as used herein, in a plane of glass having a pair of opposed faces and an edge extending between the faces, the height of the bevel is measured along the edge transverse to the faces, the bevel width is measured along the plane of the faces transversely from the edge, and the bevel angle is measured between the plane of one of the faces and the produced bevel.
Conventional glass beveling machines come in two general forms. The first is a single-headed machine, which is commonly called a shape beveling machine. The machine supports a pane of glass and rotates it with respect to a grinding head. The head rotates at a fixed bevel angle with respect to the edge region of the pane to bevel the edge region as the pane is rotated with respect to the head. The bevel angle of the head is adjustable prior to use to control the height and width of the resulting bevel, but remains at a determined angle when the machine is being used. As a result, the produced bevel has a constant height and width along the edge region of the pane. The machine may include positioning rollers that follow or trace the edge of the glass to orient the head with respect to the edge region. Other embodiments of this type of machine use a template that is followed or traced to define the path of the head. These machines are useful because they can bevel the entire perimeter of a pane of glass as the pane is rotated with respect to the head. However, the machines are rather slow and labor intensive because the single head requires multiple passes with a variety of heads to completely bevel and polish the edge region of the glass. In addition, these machines only work with panes of glass that do not have sharp corners so that the tracer can follow the perimeter of the glass. Examples of these machines are illustrated in U.S. Pat. Nos. 4,989,323, 5,028,182, 5,074,079, 5,265,382 and 5,433,652 to Park, the disclosures of which are hereby incorporated by reference.
The other general type of conventional beveling machine is a multi-headed machine that is commonly referred to as a straight beveling machine. The machine is much faster than the above-described tracing machine, however it is only suited for use on glass plates or panes that have straight edges. The machine includes a plurality of spaced-apart heads (typically at least nine) and a track or feed path along which the glass plate is fed through the machine and into contact with the heads. The heads collectively bevel and polish one edge of the plate at a time, and the heads typically are arranged to begin with rather coarse grinding heads and end with polishing heads. The machine may also include an edging head that "seams" the edge of the work piece so the edge is not sharp. In some embodiments, the heads are adjustable, in that they may be positioned prior to use to adjust the bevel width, bevel angle and to accommodate the fact that glass plates come in a variety of thicknesses. After being initially positioned, however, the heads remain fixed in their defined positions while the glass pane is fed through the machine.
One specific type of bevel is a wave bevel, in which either or both of the height and the width oscillate along the length of the edge region of the pane of glass. Typically, the oscillating width and/or height periodically vary along the length of the edge region, however, in some embodiments the wavelength and degree of variance are not constant. Wave bevels further improve the appearance of a pane of glass over conventional bevels, but they are much more difficult to produce, especially on a pane of glass with straight edges.
Before the invention disclosed herein, it was only possible to produce a wave bevel using the temple-following form of a single-headed beveling machine. This type of machine can be adapted to produce wave bevels when an appropriate template is used to cause the head to move in and out with respect to the edge. Because of the single head, however, it is necessary to make repeated passes along the edge region of the work piece with a variety of treatment heads to produce the finished wave bevel. Generally, the initial pass is made with a fairly coarse grinding head, then that head is replaced with a somewhat smoother head and the grinding process is repeated. This process is repeated a number of times with less abrasive grinding heads, including very smooth polishing heads.
Because of the number of times the work piece must be engaged by the heads, as well as the time needed to remove and replace each of the treatment heads, the above-described process is extremely slow and labor intensive. This causes the wave beveled glass to be much more expensive than a conventionally beveled pane of glass. By way of example, a pane of glass with a simple bevel may be three times as expensive as a similar pane without beveling, and a pane of glass with a wave bevel may be three times as expensive as a similar pane with a simple bevel. Furthermore, because existing wave beveling machines must follow a template to position the treatment head with respect to the edge region, they cannot easily produce a wave bevel on the corner regions of the pane of glass. More specifically, the head cannot properly maneuver around a corner without losing contact with the edge or the template. Therefore, each of the generally straight edges forming the corner must be separately beveled, thereby further increasing the time and labor necessary to produce a wave bevel along the entire perimeter of the pane of glass.